Conventionally, a screw device is composed of a screw shaft having a spiral rolling body rolling surface formed in an outer peripheral surface thereof, a nut member formed with a spiral loaded rolling surface formed in an inner peripheral surface thereof so as to face the rolling body rolling surface with the same lead angle as that of the rolling body rolling surface, and a number of rolling bodies interposed between the loaded rolling surface and the rolling body rolling surface and rolling in a loaded state, and an endless track for circulating the rolling bodies is formed to the screw device.
As a method of constituting such endless track for the rolling bodies, some of methods or systems have been conventionally provided, for example, including an external circulation system using a return tube, a spinning system using a deflector, an interior circulation system using a side lid, and the like. (For example, refer to Patent Documents 1 and 2, mentioned hereinafter).
However, in these systems, at a time when the rolling body is moved from a terminal end of the endless track to a non-loaded area, the rolling body collides with a side wall of a direction changing passage formed obliquely with respect to an advancing direction of the rolling body at the terminal end of the loaded area, that is, a tangential direction along the lead angle of the loaded rolling surface, then the rolling body, now in rolling, is scooped in the direction changing passage such as return tube forming the non-loaded area, and finally, is circulated again to the start end of the loaded area.
Accordingly, in such conventional screw devices for the rolling bodies, in spite of the systems constituting the endless tracks of the rolling bodies, there was needed means for changing the rolling direction of the rolling body at the time of scooping the rolling body in the non-loaded area rolling in the loaded or feeding the rolling body in the non-loaded area to the loaded area, and therefore, the smooth circulation motion of the rolling body is essentially impaired, and as a result, uniform and stable rotational motion of the rolling body screw device was impaired, usable lifetime was shortened, and undesired noise was caused.
Then, in order to solve the above-mentioned defects encountered in the conventional technology, the applicant of the subject application has been conceived and provided an end-cap type rolling body screw device in which a member corresponding to a conventional side lid was composed of a plurality of members including a side lid body and a return piece, and ideas were applied to shape and locating position of the return piece so as to form the non-loaded area in the endless track aiming the stable circulation of the rolling body (refer to Patent Document 3, mentioned hereinafter). The rolling body screw device of the end-cap type provided by the applicant of the subject application can realize smooth circulation motion of the rolling body, which hence contributed to the uniform and stable rotational motion of the rolling body, the long usable lifetime, and the reduction of noise at the operation time of the device.                Patent Document 1: Japanese Utility Model Application Laid-open Publication No. SHO 49-64672        Patent Document 2: U.S. Pat. No. 4,148,226        Patent Document 3: Japanese Patent Application Laid-open Publication No. HEI 11-51145        